“MPEG” generally represents an evolving set of standards for video and audio compression developed by the Moving Picture Experts Group. The need for compression of motion video for digital transmission becomes apparent with even a cursory look at uncompressed bitrates in contrast with bandwidths available. MPEG-1 was designed for coding progressive video at a transmission rate of about 1.5 million bits per second. It was designed specifically for Video-CD and CD-i media. MPEG-2 was designed for coding interlaced images at transmission rates above 4 million bits per second. The MPEG-2 standard is used for various applications, such as digital television (DTV) broadcasts, digital versatile disk (DVD) technology, and video storage systems. MPEG-4 is designed for very low-bit rate applications, using a more flexible coding standard to target internet video transmission and the wireless communications market.
The MPEG4 video compression standard allows content-based access or transmission of an arbitrarily-shaped video object plane (VOP) at various temporal and spatial resolutions. MPEG4 supports both object and quality scalability. Fine granularity scalability (“FGS”) is one type of scalable coding scheme that is adopted by the MPEG4 standard. The FGS encoding scheme allows an MPEG4 bitstream to be encoded in two layers: the base layer, which encodes each frame with a fixed lower bound bit-rate; and one or more enhancement layers, which encodes the difference between original picture and the reconstructed base layer picture. The enhancement layer is encoded via a bitplane coding scheme, therefore enhancement layer bitstreams are scalable in the sense that an arbitrary (fine grained) number of bit-planes of the enhancement-layer can be transmitted to the decoder depending on the transmission bandwidth. The FGS coding scheme has been finalized by MPEG4 version 4.
The MPEG-4 decoder may decode only the base layer or the base layer and any subset of the FGS enhancement layer. This is useful when the decoding device is of limited or variant bandwidth and for storage purposes.